1. Field of the Invention
This invention relates to a radiation detector, such as an X-ray detector or a gamma-ray detector, and, more particularly, to a solid state radiation detector capable of developing an electric signal in response to radiation.
2. Description of the Related Art
X-ray detectors are used in such fields as X-ray crystallography, surgical and diagnostic procedures and inspection techniques, for example, and are required to have high quantum efficiency, high resolution, and sharp response.
Several types of solid state X-ray detectors are presently available. For example, a lithium doped Si detector disclosed in R. Clarke et al., Rev. Sci. Instrum. 60, 2280 (1989) is used to detect X-rays in the spectral region below 5 keV. The efficiency of this detector is very low, e.g., about 0.01%. Further, the efficiency decreases with time due to damage caused by X-ray irradiation.
A micro-channel plate (NCP) type detector is described in R. Polichar et al., "X-Ray Detector Physics and Applications", SPIE, Vol. 1736, p. 42 (1992). This NCP type detector requires a power source capable-of applying a high bias voltage in the order of kilovolts (kV). Further, a response time is of the order of milliseconds (ms) and the efficiency is about 0.02%.
A monolithic linear arrays type detector is described in "X-Ray Detector Physics and Applications", SPIE, Vol. 1736, p. 42 (1992). This type detector also requires a high voltage power source, e.g., kV order, and a response time is of the order of microseconds (.mu.s) and the efficiency is about 0.01%.
There is a need, therefore, for improvements in such detectors to provide higher efficiency and sensitivity, to enable operation at low bias voltages, under high temperatures, and without damage due to exposure to X-rays, and to provide a short response time.